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55 G. Hya, HD74688, HIP42951

55 G. Hya is a blue to white eclipsing binary system star that can be located in the constellation of Hydra. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it. The star has an estimated age of 2.10 Billion of Years but could be as young as 1.90 to 2.30 according to Hipparcos.

HIP42951 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD74688. The Id of the star in the Gould Star Catalogue is 55. Stars in the southern hemisphere are more likely to have a Gould Id than the northern hemisphere. For example, there are no Gould classified stars in Ursa Major.

55 G. Hya has alternative name(s), MX Hya.

Location of 55 G. Hya

The location of the star in the galaxy is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For 55 G. Hya, the location is 08h 45m 20.77 and -02d36`03.7 .

Proper Motion of 55 G. Hya

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -8.94 ± 1.76 miliarcseconds/year towards the north and 0.76 ± 2.64 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Age, Radius) of 55 G. Hya

55 G. Hya has a spectral type of F2+.... This means the star is a blue to white star. The star is 7436.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24253.5062598400000000s. The star has a B-V Colour Index of 0.52 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,064 Kelvin.

55 G. Hya Radius has been calculated as being 3.85 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,678,259.52.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 2.72. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is 0.23 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

The stars age according to Hipparcos data files put the star at an age of about 2.10 Billion years old but could be between 1.90 and 2.30 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

55 G. Hya Apparent and Absolute Magnitudes

55 G. Hya has an apparent magnitude of 6.41 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of 1.71 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.46. Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Distance to 55 G. Hya

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 11.50 which gave the calculated distance to 55 G. Hya as 283.62 light years away from Earth or 86.96 parsecs. It would take a spaceship travelling at the speed of light, 283.62 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

In 2007, Hipparcos data was revised with a new parallax of 16.19 which put 55 G. Hya at a distance of 201.46 light years or 61.77 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.

The star's Galacto-Centric Distance is 7,436.00 Parsecs or 24,253.51 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of 55 G. Hya

The star is a eclipsing binary system Beta Persei (Algol) variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. 55 G. Hya brightness ranges from a magnitude of 7.010 to a magnitude of 6.520 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.8 days (variability).

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

55 G. Hya Facts

Alternative Names

Traditional/Proper Name55 G. Hya
Short NameMX Hya
Hipparcos Library I.D.42951
Bonner DurchmusterungBD-02 2676
Gould I.D.55
Henry Draper Designation74688

Visual Facts

Star Type star
Age2.10 Billion Years Old
Age Range1.90 - 2.30 Billion Years Old
Absolute Magnitude1.71 / 2.46
Visual / Apparent Magnitude6.41
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)08h 45m 20.77
Declination (Dec.)-02d36`03.7
Galactic Latitude23.78 degrees
Galactic Longitude229.28 degrees
1997 Distance from Earth11.50 Parallax (milliarcseconds)
 283.62 Light Years
 86.96 Parsecs
2007 Revised Distance from Earth16.19 Parallax (milliarcseconds)
 201.46 Light Years
 61.77 Parsecs
Galacto-Centric Distance24,253.51 Light Years / 7,436.00 Parsecs
Proper Motion Dec.-8.94 ± 1.76 milliarcseconds/year
Proper Motion RA.0.76 ± 2.64 milliarcseconds/year
B-V Index0.52
Radial Velocity-14.40 ± 0.20 km/s
Iron Abundance0.23 ± 9.99 Fe/H
Spectral TypeF2+...
Colour(F) blue to white

Variable Star Details

Variable Star ClassEclipsing binary system
Variable Star TypeBeta Persei (Algol)
Mean Variability Period in Days0.796
Variable Magnitude Range (Brighter - Dimmer)6.520 - 7.010

Estimated Facts

Calculated Effective Temperature6,064 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.


Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
74688-02 2676.0A6.60000-6.00000-6.00000F5Yellow/White
B7.60000-28.00000-27.000001830

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